Noncontact printers which utilize droplets emitted from an orifice plate are generally known in the art as shown by U.S. Pat. Nos. 3,373,437 to Sweet et al; 3,560,988 to Crick; 3,579,721 to Kaltenbach; and 3,596,275 to Sweet. Typically, fluid filaments of ink, dye or the like (hereinafter "fluid") pass through the orifices of an orifice plate, and a first array of individually controllable electrostatic charging electrodes are disposed downstream of the orifice plate along a "droplet formation zone" to selectively charge droplets of the fluid. The droplets subsequently pass through an electrostatic field which deflects the charged ones of the droplets from the normal path towards a droplet catcher. Uncharged droplets proceed along a normal path and are deposited upon a receiving substrate.
Typically, noncontact ink jet or "fluid jet" printers use a solvent-based ink or dye medium which contains water as the principal component. Many of the dye compositions used in fluid jet printing operations are formed by dissolving a solid dye material in the aqueous solvent medium. In other compositions, the fluid is comprised of a dispersion of fine particles in a liquid, such as disperse dyes commonly used in dyeing textiles. Typically, the ink supply system for the printer includes a fluid reservoir or supply chamber disposed above the orifice plate which connects to a fluid manifold assembly. The manifold distributes an even flow of printing fluid across the linear array of orifices and is generally secured to the orifice plate by using mounting clamps, brackets or the like. Once assembled, the manifold and orifice plate define a "dye cavity" for the dye medium used during the print operation. In this regard, the present method and apparatus for ultrasonically cleaning the fluid jet components is particularly useful for cleaning the orifice plate/dye cavity structures described and claimed in commonly-owned U.S. application Ser. No. 750,589, the disclosure of which is hereby incorporated by reference.
During the assembly of the orifice plate and manifold structure, tiny metal particles, dust or other solid particulates may become trapped in the assembly at or near the bearing and seating surfaces for metal components, particularly when the clamps are tightened against the orifice plate. The particles are thereafter introduced into the dye cavity and/or the openings of the orifice plate itself. In addition, during normal operation of the fluid jet printer, particles of dried ink or disperse dye may become lodged in or adjacent to the orifices or even collect on the inside surfaces of the fluid reservoir, dye cavity and related parts of the print head assembly.
The problem of solid particulates in the fluid becomes particularly significant in fluid jet devices in which certain of the droplets not deposited on the print substrate are caught by a catcher structure (or "gutter" assembly). The so-caught fluid droplets (containing undesired solid particulates) are usually recirculated to the fluid supply system for reuse in a subsequent printing operation. Invariably, contaminants such as dust, lint and the like are introduced into the fluid supply system and are not removed by conventional fluid filtration means. Such solid particulates may "settle out" and attach to portions of the fluid supply system forming undesired deposits.
Particles within the deposits may also break loose and migrate to other portions of the fluid supply system causing clogging or contamination. In particular, the solid particles in the fluid may block or partially hinder the flow of fluid through one or more of the orifices, Obviously, if an orifice is partially or totally blocked, the normal throughput of fluid for deposition on the substrate may change. In addition, a blocked orifice may result in imperfect droplet trajectories and/or variations in the charging/deflection mode of the printer, thereby reducing the accuracy of placement of the droplet on the substrate. In printing or dyeing operations this could result in quality degradation.
Recently, it has been proposed to utilize a fluid jet apparatus as a means to print patterns or the like on textile materials, such as the fluid jet printing device disclosed in commonly-owned U.S. Pat. No. 4,523,202, the disclosure of which is also expressly incorporated herein by reference. Fine printing of patterns on a textile substrate is achieved by the use an orifice plate having at least one linear array of very small orifices sized in the range of, for example, 0.00035 to 0.020 inches in diameter equally spaced from one another on the order of fifty to two hundred per inch. It is highly desirable in the use of such small diameter, high density orifices spaced for purposes of forming print patterns on textile substrates that any particles or residue which might otherwise clog an orifice or change its configuration be eliminated or reduced to an absolute minimum.
A number of methods have been used in the past for cleaning an ink jet printing head without removing the print head from the printing structure, such as those shown by U.S. Pat. Nos. 4,007,465 and 4,276,554. In addition, various approaches have been used for providing an ultrasonic vibration to assist in dislodging trapped solid particles at or near the orifice openings. Certain arrangements, for example, increase the ink pressure upstream of the orifice while vibrating a nozzle or orifice structure. Other proposals use vibration means coupled with heat at or near the nozzle or orifice.
However, none of the prior arrangements are entirely effective for removing particles or residues which might otherwise block the orifice openings, particularly under circumstances where the orifice plate uses small, closely-spaced orifice openings. In particular, the prior devices are incapable of preventing ink clogs caused by contaminants introduced, for example, when the orifice plate is initially fastened to the manifold assembly before being placed in operation, or during a routine maintenance function such as when a filter for the fluid supply is replaced without shutting down and cleaning the entire fluid supply system. For closely-spaced, high density orifice plate structures, the prior methods of ultrasonic cleaning are also ineffective in removing solidified ink which forms ink deposits during long periods of non-use, or the fine dust particles and atmospheric impurities in the ink supply which may ultimately cause the entire ink jet head to malfunction or perform to a degree that is less than satisfactory. Prior methods and apparatus are particularly unsuited for cleaning orifice plate assemblies for textile applications in which the orifice array is on the order of 1.8 meters long.
It has now been found that the above problems relating to the clogging of orifices in fluid jet devices may be substantially eliminated by the method and apparatus according to the present invention. In particular, applicant has discovered a method for cleaning the ink jet printing orifices of the orifice plate of a printing head which serves as the final step in the initial assembly of the print head, i.e., at the critical time when small, solid particulates are generated by the assembly process itself. In essence, the improved method of ultrasonic cleaning according to the invention includes the steps of placing the orifice plate/dye cavity assembly into a tank containing a quantity of cleaning fluid. The tank is then agitated at a ultrasonic frequency to cause cavitation of the cleaning fluid, thereby dislodging foreign particles from the entire orifice plate/dye cavity assembly. Simultaneously, a filtered fluid stream is directed through the orifices of the orifice plate in a direction opposite the normal flow of fluid through the orifices by pumping cleaning fluid out through ink supply inlets on the opposite side of the orifice plate/dye cavity assembly. The combination of ultrasonic fluid cavitation and reverse flow causes particles to be dislodged from the orifices and the ink/dye cavity. The solid particulates are then carried by the reverse-directed fluid stream away from the orifices and out of the inlet tubes of the dye manifold so that they cannot fall back toward the orifices themselves. The dislodged solid particulates on the exterior of the orifice plate/dye cavity assembly may be removed through a separate cleaning fluid outlet in the ultrasonic agitation tank itself or through the orifices into the cavity to be carried off by the reverse-directed fluid stream. Alternatively, the exterior may be cleaned before the interior.